The present invention relates to a corneum layer stabbing device usable to measure the chemical components of an interstitial fluid produced by suction, particularly to collect a tissue fluid below the corneum of a skin.
It has been customary to measure the contents of glucose, lactate, urea nitrogen and other chemical substances existing in an organism by collecting blood. The content of each component is measured on the basis of a change in the color of a test paper, a light absorption degree, or an electric signal output from a biosensor. Such measuring methods have recently been improved to such an extent that even a sample of several microliters can be measured. To collect blood, a needle is usually penetrated into the vein of, e.g., an arm. On the other hand, when the amount of blood necessary for measurement is only several microliters, a fine needle having an inside diameter as small as several microns may be penetrated into a capillary. However, it is difficult to accurately position and insert such a fine needle into a capillary. In light of this, a method using a blood collecting device having a number of fine hollow needles has been proposed in, e.g., Japanese Patent Laid-Open Publication No. 7-132119. This method makes it needless to position a single needle.
On the other hand, measuring methods using an interstitial fluid collected from a skin in place of blood have been proposed and disclosed in, e.g., Proc. of the First Pan Pacific Symposium, Vancouver, Canada, Jul. 23-27, 1986, pp. 57-58 and Proc. of the Symposium of the Chemical Sensors, PV87-9, pp.327-333.
An interstitial fluid is a trace of liquid produced by removing a corneum layer from a part the skin of, e.g., an arm and then depressurizing the same part. The interstitial fluid is generally considered to be a fluid existing in a hypodermic tissue or a liquid filtered via a capillary wall due to depressurization. Because the interstitial fluid produced by suction is lower in a protein content than blood, it reduces the deposition of proteins on the surface of a sensor during measurement and thereby extends the life of the sensor. In addition, collecting an interstitial fluid via a skin reduces the subject's pain and contagion, compared to the collection of blood. This kind of method is taught in, e.g., Japanese Patent Laid-Open Publication No. 4-341241 by way of example.
The conventional blood collecting device has a problem that needles are formed by a silicon nitride film as thin as 1 .mu.m and therefore extremely fragile and cannot easily penetrate a skin. Another problem is that the needles penetrated a skin are apt to bend and stop holes or to be left in the subject's body. Moreover, when blood is passed through a fine tube whose diameter is as small as several tens of microns, red blood cells present in the blood and having a diameter of about 10 .mu.m to 20 .mu.m are destroyed (hemolysis). This changes the contents of chemical substances existing in the blood.
The conventional method of measuring an interstitial fluid produced by suction solves the above problems, but brings about other problems, as follows. A first problem is that a tape stripping method used to remove the corneum layer needs expertness. Specifically, the thickness of a corneum layer and how it comes off depend on the portion, age and sex. Should the removal of a corneum layer be insufficient, an interstitial fluid would not be collected. Should the removal be excessive, it would cause bleeding and pain to occur. Therefore, to remove a corneum layer to a depth great enough to collect an interstitial fluid without any bleeding, careful operation relying on experience and perception is necessary.
A second problem is that the removal of a corneum layer is a burden on a subject or patient both physically and psychologically because the patient is required to stay still for more than 30 minutes until the end of the removal.
A third problem is that a skin does not cure rapidly.
That is, a skin from which a corneum layer has been removed does not regenerate for about two weeks.
A fourth problem is that it is difficult to remove a corneum layer evenly, resulting in inefficient interstitial fluid collection. Specifically, the amount of collection of an interstitial fluid is proportional to the area of removal of a corneum layer. In a corneum layer, basement cells below corneum repeat division with the result that keratinocytes are stacked on a skin in the form of scales. The tape stripping method renders the removal of such a corneum layer irregular and cannot remove a desired area evenly.
Technologies relating to the present invention are also disclosed in, e.g., Medical and Biological Engineering & Computing, May 1994, pp. 242-246 and Japanese Patent Laid-Open Publication Nos. 2-286132 and 6-121796.